Prior to the commencement of production in a wellbore, it is important to test the integrity and the connections of downhole equipment and tubing. Leaks, faulty connections, or faulty equipment can lead to hydrocarbon losses during production and potentially dangerous and life-threatening situations for operators at the surface of a well. To lessen the danger, a pressure test is normally performed in which the tubing (e.g., production tubing) or drillpipe is pressurized from the surface and any leaks or faulty connections are detected by a loss of pressure as measured by a gauge also located at the surface. To successfully accomplish this test, the tubing or drillpipe must be plugged at some point downhole and be sealed from a selected formation.
The types of devices previously used to plug the tubing or pipe downhole include closed formation tester valves and tubing tester valves. Flapper valves have also been utilized for such a purpose, as illustrated in U.S. Pat. No. 4,134,455 issued to Read, U.S. Pat. No. 4,694,903 issued to Ringgenberg, U.S. Pat. No. 5,137,090 issued to Hare et al., and U.S. Pat. No. 5,188,182 issued to Echols et al. The flapper valves disclosed in the above referenced patents are generally designed to seal against pressure adjacent the upper side (e.g., pressure from the uphole side) of the flapper valve.
The ability to seal against both uphole and downhole pressure is important because pressure may accumulate in the wellbore underneath the downhole plug. Therefore, it is desirable that a flapper valve be capable of withstanding not only pressure on its upper side generated by the pressure tests, but also pressure on its underside generated by the production fluids or downhole environment.
Additionally, pressure tests are typically conducted several times in sequence, generally each time additional tubing or drillpipe has been added to a drillstring and inserted downhole. The flapper valve must maintain its sealing engagement to the relevant tubing or drillpipe throughout each of the pressure tests in order to preserve the accuracy of each test. Once the pressure tests are completed and the wellbore is ready for production, it is necessary to remove, at least partially, the downhole valve or plug in order to pass other downhole tools through the drillpipe or tubing, or to allow production fluids to flow up to the surface through the tubing or drillpipe. It is preferable to completely remove the downhole valve or plug from the bore of the tubing or drillpipe so that the downhole tools and production fluids can pass and flow freely and without obstruction.
Attempts have been made to design a downhole plug that provides for a clear bore when the valve is opened. However, most plugs (such as those in the aforementioned patents) include parts (e.g., valve seats or internal tubing) that remain in the bore after the flapper has been removed or opened. Parts that remain in the bore may obstruct the passage of tools and the flow of fluids through the bore. It is therefore desirable to provide a downhole valve which enables the complete removal of the flapper valve from the bore of the relevant body at the appropriate time and which leaves such bore free of obstructions after use.